Epithelial metaplasia: an inadequate environment for antitumour immunity?

The reason why some cancers predominantly develop in specific sites of a given organ and, particularly in metaplastic mucosal surfaces, remains obscure. Although embryologic, microbial, chemical or hormonal factors are likely to have a pathogenic role, the local immune microenvironment might also facilitate tumour growth. We propose that metaplasia, which frequently occurs in some organs (uterine cervix, respiratory tract, oesophagus and stomach), is involved in cancer development by altering the expression of soluble or adhesion molecules important for cell-mediated antitumour immunity.